Hearing aid apparatus



HEARING AID APPARATUS Original Filed March 2, 1948 ETHYL ALCOHOL PHENOL INVENTOR. HAROLD. J. M CREARY Patented Nov. 20, 1951 HEARING AID APPARATUS-: Harold J. McCreary, LombariL'Ill;

Original application March Z, 1948, Serial No. 12,561, now Patent No. 2,554,113," dated May 22, 1951. Divided'and this applicationseptember 22,1950, Serial No. 186,184

4 Claims.

' Thisapplication isga division of my copending application, SerialNo. 12,561, filed March 2,v

The invention relates to potentiometers.

In, many instances where potentiometers are employed, the adjustment thereof has been recognized as being productive. of. objectionable operating characteristics inrelated apparatus, one suchinstancebeing in hearing aid apparatus where usual orconventional potentiometers producean objectionable. sound in thesystem, such sound, usually, being termed; microphone noise- It is thereforean important object of the invention,toenable ahearin laid to be so const ruc ted thatv adjustment of ;the potentiometer does .not produce theeusual microphone noise, and an .objectrelated tothe foregoing. is toenable a po-. tentiometer to. be so, constructed that such noise that usually occurs in the adjustment of a potentiometer in an amplifier system is eliminated,

Otherandfurther objects, of thepresent in-, vention will be apparentfrom the following descriptionand claims and are illustrated in the accompanying. drawing which, by way of illustration, shows a preferredv embodiment of the present invention and theprinciples thereof and what I now consider to be the best mode in which I have contemplated applying these principles. Other embodiments of the invention embodying the sameor equivalent principles may be used and structural changes may be made as desired by those skilled in: the art without departing from the present invention, and the purviewof the appended. claims.

In; the drawing:

Fig. 1 is a front elevational view of a potentiometer embodying the invention;

Fig. 2 is a front elevational view of an operating member for the potentiometer of Fig. 1; and

Fig. 3 is a chart illustrating the electrical characteristics of one liquid mixture that may be utilized in the potentiometer of Fig. 1.

In the drawing, a potentiometer is illustrated that is particularly adapted for use in the hearing aid apparatus shown in my aforesaid copending parent application, Serial No. 12,561, now Patent 2,554,113, issued May 22, 1951 of which the present application is a division, and this potentiometer enables noise to be eliminated so as to render the hearing aid much more satisfactory in use. The noise that is thus eliminated has been termed the carbon rattle or microphone effect that is inherent in carbon strip potentiometers, and in the potentiometer shown, this is avoided through the use of a liquid resistor. Thus the potentiometer of Figs. 1 and 3 is afforded by a liquidtype container 250 made from a material such as glassto afford, an arcuate liquid chamber 251 that extends through nearly a complete circle. The ends of the container25ll are sealed as at 250A, Fig. 1, and contact terminals 252 and 253 .areextended through the respective ends of 250. Approximately midway between the ends 259A the container 259 hasa lateral extension 254 that houses a contactmember 255whereby an electrical H connection may be extended into the tubeat thispoint. Theoutersurface ofthe container 250 is silvered to afford electrostatic shielding. Within the tube 250, a shiftablew displacement member 251 is mounted, this displacement member being arranged to extend through somewhat less than and the tube or container 250 is filled with a liquid resistor. Thus by shifting the displacement member 25'! about the container 250, the effective resistance between the center contact 255 and either one of the contacts 252 or 253 maybe varied.v In order to enablethe displacement member 251 to be readily shifted, this displacement member is formed from an iron rod 2,5lA and this iron rod is housed and protectedfrom the dielectric liquid by a covering such as a glass covering251B. The displacement member 257 may thus be influenced magnetically, and in order that this may be done, the ring 36M has an arcuatepermanentmagnet 26!] molded into oneface thereof so as to extendin equal amountsin opposite directions from the upper point'defined by the handle 36H. If desired, the iron core 251Amayalso be embodied as a magnet, and henceewhen the ring 36M of Fig. 2 is disposed opposite the forward face of the potentiometer shown in Fig. 1, the displacement member 25Tmay be readily and easily shifted within the container 250 so as to vary the effective resistance between the appropriate terminals or contacts of the potentiometer. This is accomplished without the noise that is usually present in devices that are used for this general purpose. This dielectric liquid that is used may be made of the desired resistance to conform with the circuit requirements and the effective cross sectional areas of the potentiometer, and this may be accomplished by reference to the text book entitled Liquid Dielectrics, translated from the German by Karapetoff. Thus in Fig. 3 a graph is shown wherein the logarithm of p, the resistance in ohms per cubic centimetre is plotted on a logarithmic scale against percentage of volume of certain liquids. To use this diagram the resistive value required per cubic centimetre of liquid is determined by calculation from the dimensions of the elements of the potentiometer. This resistive value is then laid out on the diagram as a vertical line, and the points at which this line intersects the alcohol line and the phenol line determines the percentages of these liquids to be placed in the solution. One per cent of picric acid is also added to the solution, together with benzene in a quantity suflicient to make 100%. As an example, to attain a solution having a resistance of one hundred thousand ohms per cubic centimetre, the log of which is 5, the mixture would be:

Per cent Ethyl alcohol 40 Phenol Picric acid 1 Benzene 49' From the foregoing description it will be evident that the present invention affords a novel and advantageous potentiometer which enables potentiometer noise to be eliminated, and which improves the performance of electrical apparatus in which such potentiometer is used.

- Thus, while I have illustrated and described the preferred embodiment of my invention, it is to be understood that this is capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims. 1 1

I claim: a

1. In a potentiometer for hearing aid apparatus and the like, an elongated hollow glass tube of substantially uniform cross section, electrical contacts disposed in said tube at spaced points, a liquid within said tube having a predetermined electrical resistance, an elongated member including an insulated part made of a ferrous metal and of less length than said tube and disposed within said tube for adjusting movement along said tube to different positions to change the effective electrical resistance aiforded by said liquid between said contacts, and a magnet element mounted for movement along the outside of said tube and effective magnetically on said member to adjustably position the same in said tube.

2. In a potentiometer for hearin aid apparar tus and the like, a closed elongated hollow glass tube of substantially uniform cross section and formed to a circular arrangement wherein opposite ends are disposed adjacent each other, electrical end contacts disposed in said tube at the ends thereof, said tube having a relatively small lateral extension formed thereon near the midpoint thereof, a center contact disposed within said extension, a liquid within said tube having a predetermined electrical resistance, a glass enclosed armature of arcuate form and less length than said tube and disposed within said tube for adjusting movement along said tube to different positions to change the effective electrical resistance afforded by said liquid between said contacts, and an arcuate magnet element mounted for movement outside of and concentric with said tube and effective magnetically on said member to adjustably position the same in said tube.

3. In a potentiometer for hearing aid apparatus and the like, a closed elongated hollow glass tube of arcuate form and substantially uniform cross section, electrical end contacts disposed in said tube at spaced points, said tube having an extension laterally from one side thereof intermediate said end contacts, another contact disposed in said extension, a liquid within said tube having a predetermined electrical resistance, an armature member of less length than said tube and disposed within said tube for adjusting movement along said tube to different positions to change the eifective electrical resistance aiforded by said liquid between said contacts, and an insulating covering for said armature.

4. In a potentiometer for hearing aid apparatus and the like, a closed elongated hollow glass tube of substantially uniform cross section, electrical contacts disposed in said tube at spaced points, a liquid within said tube having a predetermined electrical resistance, an elongated liquid displacement member of less length than said tube and disposed within said tube for adjusting movement along said tube to different positions to change the elfective electrical resistance afforded by said liquid between said contacts, an armature disposed within said tube and associated with said displacement member, and a magnet element mounted for movement along the outside of said tube and effective magnetically on said armature to adjustably position the displacement member in said tube.

HAROLD J. MCCREARY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,605,666 Kronauer Nov. 2, 1926 1,625,703 Bobo Apr. 19, 1927 1,819,849 Stearns Aug. 18, 1931 2,256,833 McDonald Sept. 23, 1941 

